The present invention relates to a color conversion method and a density gradient correction method for a printer for mainly producing a color proof for forming a color image and a printer capable of performing the methods
When a color proof is produced by using a color conversion (hereinafter called xe2x80x9ccolor matchingxe2x80x9d) technology for matching a color print to printed matter, a color matching method similar to a conventional method is employed. That is, yellow (Y), magenta (M), cyan (C) and black (K) data items are first converted into data of chromaticity, and then converted into C, M, Y and K data peculiar to the printing system by using a translation table. The above-mentioned method is a known and marketed color matching method as xe2x80x9cColor Syncxe2x80x9d (trade name).
A density calibration technology for correcting the sensitivity difference of a material and a machine is disclosed in Japanese Patent Application No. Hei. 9-126108 applied by the applicant of the present invention. The density calibration technology has the structure that the intervals of the instructed halftone % are made to be constant.
The two conventional methods have the following problems. When a color proof is produced by using the conventional color matching technology, color matching of pure colors, such as red (R), blue (B), green (G), Y, M and C, sometimes causes a highlight of another color to slightly be mixed with the pure color even if the hue of the coloring material is slightly shifted from a required hue. When a user performs an operation for confirming the produced color proof by using a magnifier in order to confirm the correctness of image data, halftone-dot gradient (the following fact cannot easily visually be confirmed in a case of density gradient) encounters the following problem: although, for example, red (R) is composed of only magenta (M) and yellow (Y), cyan (C) is sometimes mixed if the hue of the coloring material is slightly shifted from a required hue after the conventional color matching operation has been performed. In this case, there arises a problem in that a user incorrectly determines that original data has an error if mixture of cyan (C) is detected when the user confirms that data is composed of only magenta (M) and yellow (Y) by using a magnifier. Although original data is free from an error, color matching sometime causes another color to sometimes be mixed with the pure color.
The second conventional technology using the density calibration has the following problem.
(1) In a case of the halftone dot gradient, whether the gradient is solid (that is, a shadow having a gradient of 100%) or 99% can easily be determined by using a magnifier. That is, white missing in a solid image can easily be detected. When a user looks the image to confirm that the image is a solid image by using a magnifier, the user detects some white missing portions. In this case, there arises a problem in that the user misunderstands that original data has an error and thus checking cannot be performed.
(2) If original data is black data, solid characters are frequently used and thicknesses must strictly be correct. If an end of a character becomes faint, it appears that a thin character has been formed. To prevent this, a gradient of 99% is insufficient. In this case, the gradient must reliably be made to be 100%.
(3) The above-mentioned problems must always be solved even if the sensitivity of the material and the machine is changed. Therefore, density calibration for compensating the difference in the sensitivity of the material and the machine must be performed.
In a case of the halftone dot gradient, (1) whether or not a dot is included in the highlight and (2) whether or not the solid image is deformed are of extreme importance. Even if intermediate gradients are somewhat shifted, larger shift is permitted as compared with the highlight and shadow. Therefore, the accuracy for density-calibrating the highlight and the shadow must be improved.
(4) The sensitivity of a recording material for a second color is sometimes higher than that for a primary color. In this case, there arises a problem in that the margin for continuously reproducing the gradient in the secondary or higher color becomes insufficient for the highlight portions when the density calibration of the primary color is performed.
Since the sensitivity performance is different because of the difference in the material and the machine, shadow cannot sometimes be formed if the material and the machine have low sensitivity. When the material and machine have high sensitivity, highlight cannot sometimes be formed.
(5) Hitherto, weak energy has been supplied to a head to heat a non-image portion so as to prevent mixture of a dot with the highlight from taking place. In this case, a dot is undesirably added to even a non-image portion if the color is secondary or higher color and a highlight image is formed.
The present invention attempts to solve the above-mentioned problems and an object of the present invention is to provide a density gradient correction method with which a user does not misunderstand that original data has an error and which is capable of forming highlight to shadow regardless of the difference in the material and the machine and whether or not the color is a secondary or higher color.
To achieve objects, according to first aspect of the present invention, three or more dimensional color conversion is performed such that when at least one color of coloring materials, that is, a specific color such as C, M, Y, K, R, G, B or gold, is 0%, the at least one color is 0%.
According to a second aspect of the invention, the difference in energy is enlarged for only a solid gradient of a shadow portion as compared with that for a usual gradient.
According to a third aspect of the invention, the density gradient correction method of the second aspect is arranged in such a manner that the difference of only K is enlarged as compared with the differences of C, M and Y.
According to a fourth aspect of the invention, a method comprises the step of performing density calibration by using a density calibrating patch having a structure that calibrations in the vicinity of a highlight portion and a shadow portion are fine.
According to a fifth aspect of the invention, there is provided with a density-calibrating patch having a structure that calibrations in the vicinity of a highlight portion and a shadow portion are fine.
According to a sixth aspect of the invention, a method comprises the step of: providing a margin width for a highlight portion and a shadow portion. In this case, the margin width for the highlight portion is wider than that for the shadow portion.
According to a seventh aspect of the invention, a method comprises the step of also supplying weak energy to a head corresponding to a non-image portion in a case of a primary color such that the intensity of the weak energy does not cause a dot to be printed in the non-image portion in a case of-a secondary or higher color.